The present invention relates to a sun tracking system for aligning a body with the sun.
Many devices, such as parabolic reflectors, fresnel lenses, various hot air or solar engines, and solar collectors require that the device be accurately aligned with the sun to function efficiently. It is thus desirable, to maintain a solar collector in continual alignment with the sun, tracking the relative movement of the sun throughout the entire day. However, the track that the sun follows from sunrise to sunset varies on a daily basis. Accordingly, tracking means responsive to the actual position of the sun must be utilized.
The prior art tracking systems have generally been extremely complex and expensive. Examples of prior art sun tracking systems are described in U.S. Pat. Nos. 3,098,934 issued in 1963 to Wilson et al., 3,177,367 issued in 1965 to Brown, 3,305,686 issued in 1967 to Carter et al., 3,891,843 issued in 1975 to Parkin, 3,917,942 issued in 1975 to McCay, 3,986,021 issued in 1976 to Hitchcock and 3,996,917 issued in 1976 to Trihey. Other systems utilize two photocells facing the sun and relatively disposed at an angle of 60.degree.. The photocells are connected in a bridge circuit, and when one cell receives more radiation than another the circuit becomes unbalanced. A driving motor is activated in the appropriate direction until equilibrium is restored by pointing the cells directly into the sun. It should be appreciated, however, that the relative disposition of the photocells in such a system is relatively critical, and hence requiring close tolerance manufacturing processes.
The present invention provides a simple and inexpensive sun tracking system, not requiring close manufacturing tolerances or complex compensation circuitry. Briefly, the present invention utilizes an angled reflective surface to produce a discrete spot of light on a predetermined surface, in fixed relation to the reflective surface. The position of the spot of light on the predetermined surface is indicative of the relative position of the sun with respect to the reflective surface. The reflective surface and predetermined surface are fixed to the body to be aligned with the sun. A photo-sensitive device is mounted on the predetermined surface at a position illuminated by the spot when the reflective surface, and hence the body, is at the desired alignment with the sun. The photo-sensitive device is utilized to inhibit an otherwise activated motor.
When the sun moves out of alignment with the reflective surface, the photo-sensitive device is no longer illuminated, and the motor, no longer inhibited, effects a rotation of the device in the direction of the sun's travel until the spot once more illuminates the photo-sensitive device to again inhibit the motor. In the preferred embodiment, as will be described, a second photo-sensitive device is disposed in close proximity to the first and used to effect a positive activation of the motor in compensation for changes in ambient light. Limit switches are utilized to define the tracking range, and to cause the unit to be restored to an initial position, e.g., an easterly-most position in the morning.
The predetermined surface can be disposed so that is not directly illuminated by sunlight. However, it should be appreciated that such a disposition is not necessary when utilizing separate inhibit and activation photo-sensitive devices in that the effects of ambient light can be cancelled, as will be explained. Further, additional photo-sensitive means can be included to inhibit the operation of the device when the ambient light is below a given threshold value, e.g., during the night.